The discovery of high temperature superconductive materials in the late 1980's was soon followed by a desire to form such materials into wires, tapes or similar shapes. Ideally such wires or tapes should be physically strong, flexible, highly conductive and able to withstand strong magnetic fields without loss of current carrying capacity.
Processes generally referred to as "powder in a tube" have been developed. For example, a general process of fabricating superconductive wire involves initially preparing a superconductive powder, filling a tube or pipe of silver with the superconductive powder, sealing the pipe or tube, subjecting the pipe or tube to reducing or deforming operations to form wire, and finally sintering the reduced wire.
Generally, conventional deformation processing provides long lengths of a desired form such as rod, wire, tube or tape, consolidates the superconductor powder, and induces a desirable texture into the high temperature superconductive material (referred to as Deformation Induced Texture--DIT). High relative densities and sharp textures in the superconducting phase are required attributes for all high performance high temperature superconductive conductors. Certain high temperature superconductive materials show marked texturing via certain methods of deformation processing. It is well known that high performance high temperature superconductive conductors that contain Bi-2223 are fabricated using an iterative thermomechanical process in which certain types of deformation are interspersed with high temperature heat treatments. The deformation provides the desired density and texture in the high temperature superconductive material and the heat treatments result in chemical reactions that heal microcracks. Ultimately, the result is a composite within which the Bi-2223 grains are textured and connected.
Previous techniques have focused on wire drawing and tape rolling to achieve high density and texture. Such processes have routinely been performed at room or ambient temperatures or at elevated temperatures. Although high performance conductors have been fabricated using a deformational process at room temperature, microstructural analysis of the resultant composites continues to indicate that there is much room for improvement. Accordingly, alternatives to the conventional processing were sought whereby improvement in the properties of the resultant high temperature superconductive composites could be realized.
An object of the present invention is to provide an improved reduction or deformation process for the preparation of high temperature superconductive wires or tapes.
Another object of the present invention is to provide such a reduction or deformation process for the preparation of high temperature superconductive wires or tapes whereby improvements in texture and uniformity of the superconductive material thickness, increased filament uniformity and increased density of the superconductive material can be achieved.
Still another object of the present invention is to provide, via an alternative reduction or deformation process, a high temperature superconductive composite having a higher density of the superconductive material and an improved uniformity of superconductive thickness in the composite as well as improved filament uniformity.